Waveguide CO2 lasers are lasers in which lasing modes are constrained in zigzag arrangement of waveguide channels machined in a ceramic slab. Aluminum oxide (alumina—Al2O3) is the most commonly used ceramic material for the waveguide slab, for reasons including ease of machinability and a low cost relative to other machinable ceramics. The aluminum oxide ceramic slab is bounded by electrodes for exciting an RF discharge in a lasing gas in the waveguide channels. The RF discharge energizes the lasing gas for providing optical gain. A plurality of mirrors provides a folded laser resonator having a resonator axis extending through the zigzag arrangement of waveguides. Waveguide CO2 lasers can be arranged to emit radiation at a wavelength within certain characteristic bands of wavelengths extending from about 9.2 μm to 10.8 μm. A particular laser wavelength is typically selected by the use of wavelength selective reflective coatings for the resonator mirrors. The most common CO2 laser wavelength is 10.6 μm.
Wavelengths between about 9.2 μm and 9.7 μm are particularly useful for laser drilling in printed circuit board (PCB) materials. This is because these materials have a greater absorption for wavelengths in this wavelength range than for longer wavelengths. Unfortunately, the average power output for a pulsed waveguide CO2 laser operating at a wavelength between about 9.2 μm and 9.7 μm is significantly less than for the same laser operating at 10.6 μm. By way of example, a Coherent-DEOS™ model LC-40 operating in a continuous wave (CW) mode at wavelength of 10.6 μm is capable of delivering an average power of about 40 Watts (W). The same laser operating at a wavelength of about 9.7 μm is capable of delivering only about 3 W. There is a need for increased average power output for waveguide CO2 lasers operating at wavelengths between about 9.2 μm and 9.7 μm.